Jsonify: handle undefined in array.

[darcyparker]

Fixes #309

@bbrk24 - Please review and suggest tests if you see anything I missed.

I did not address Jsonify<{ x?: string }>. This seems to be a harder problem.

I experimented with

type RequiredKeys<T> = {
	[K in keyof T]-?: (
		{} extends {[P in K]: T[K]} ? // {} extends optional, but not required
		never :
		K
	)
}[keyof T];

type OptionalKeys<T> = {
	[K in keyof T]-?: (
		{} extends {[P in K]: T[K]} ? // {} extends optional, but not required
		K :
		never
	)
}[keyof T];

type JsonifyObject<T extends object> =
	{[P in RequiredKeys<T>]: Jsonify<T[P]>} &
	{[P in OptionalKeys<T>]?: Jsonify<Exclude<T[P], undefined>>;};

And adding JsonifyObject<T to Jsonify<T>...

But as I started to write tests, I realized I have an issue with JsonObject's implementation

// Special cases of Object with optional member
declare const objectWithUndefinedValue: {x: undefined};
declare const parsedStringifiedObjectWithUndefinedValue: Jsonify<{x: undefined}>;
expectNotAssignable<JsonValue>(objectWithUndefinedValue); //I expected this to pass
expectAssignable<JsonValue>(parsedStringifiedObjectWithUndefinedValue);
expectAssignable<{}>(parsedStringifiedObjectWithUndefinedValue);

declare const objectWithOptionalValue: {x?: string};
expectAssignable<JsonValue>(objectWithOptionalValue);

I feel #65 had the right idea and should allow optional key-value pairs, but not a key-value pair where the value is undefined.

I need to come back to this... but wanted to leave the above notes if someone else wants to take a crack at it.

[bbrk24]

One minor suggestion for the test, other than that everything looks good.

[bbrk24]

Since it's expecting null[], I think it should test Jsonify<undefined[]> for consistency.

[darcyparker]

I am not sure what you mean.

I am verifying Jsonify<undefined[]> is the expected null[].

expectType<Jsonify<undefined[]>(parsedStringifiedArrayWithUndefined1); would be true if the implementation of Jsonify was wrong.

[bbrk24]

I am verifying Jsonify<undefined[]> is the expected null[].

I am saying that it should do that. However, it currently doesn't test Jsonify<undefined[]>, it tests Jsonify<[undefined]>.

Ultimately it isn't a big deal, I just didn't see any point in using a tuple.

[darcyparker]

Ah - I get what you're saying now. Thanks. I will make that correction when I get back to this problem.

[darcyparker]

Addressed in 68474d1

[sindresorhus]

Note that #312 was merged.

[sindresorhus]

It's unclear to me whether this is still needed after #312?

[darcyparker]

I think this is still relevant. It handles undefined in array correctly. See #309 where it was noted that "undefined in an array becomes null". I am sorry this sat in draft. #312 does solve the other part of #309.

https://github.com/sindresorhus/type-fest/pull/310/files#r743986229 has a small comment about the tests. I tested [undefined] and not the more general undefined[].

[darcyparker]

@sindresorhus - Updated and ready for review.